It is desirable to obtain high RF power amplifier efficiency in many practical applications. At least one, if not all, of the following requirements is important: low power consumption (especially for battery-operated equipment), low temperature rise of the components, high reliability, small size, and light weight. Although the parasitic energy losses in, for example, inductors and capacitors are sometimes important, the major power loss in power amplifiers is usually due to power dissipated in the transistor(s). This was true for the Class A, B, and C PAs (their theoretical collector efficiency was calculated in Sections 2.1 through 2.3).